i think both are really directly related. I mean, I've heard songs that have crap lyrics but sounded great, and also some songs that were just thrown together around some awesome lyrics, maybe even a poem. Then again, I don't mind a good instrumental, but I can only take so much. You don't want such a gap in your music that it makes the audience forget what they're listening to, unless that's what you're going for. Jamming is fun for the band, granted, and some people really dig that stuff, but for the most part, I think a band should try an engage its audience as much as possible.